1. Field of the Invention
The present invention relates to a foreign substance removal apparatus capable of eliminating a foreign substance such as dust or dirt, and an optical apparatus including the foreign substance removal apparatus.
2. Description of the Related Art
In optical apparatuses such as digital cameras, the optical apparatus converts an object image into an electric signal to capture the object image, receives an imaging light flux on an image sensor, and converts the photoelectrically converted signal output from the image sensor into image data. Such an imaging apparatus includes an optical low-pass filter and an infrared absorption filter disposed at the object side of the image sensor.
When a foreign substance such as dust or dirt is attached to any of the surfaces of these filters, this results in generation of a black spot in a captured image from the attached portion, thereby deteriorating the visibility of the image.
Especially, in interchangeable-lens digital single lens reflex cameras, mechanically operating units such as a shutter and a quick return mirror are disposed in the vicinity of the image sensor, so that a foreign substance such as dust or dirt produced from these operating units may be attached to the surface of an optical member such as the image sensor and the filter. Further, at the time of a lens exchange, a foreign substance such as dust or dirt may enter from an opening of a lens mount into a camera main body, and may be attached to the surface of the optical member eventually.
To prevent this phenomenon from occurring, it is known to vibrate the optical member disposed at the object side of the image sensor with use of a piezoelectric element to remove the foreign substance such as dust or dirt attached on the surface of the optical member.
Japanese Patent Application Laid-Open No. 2008-207170 discusses a technique of generating a travelling wave at an optical member by causing a first bending vibration and a second bending vibration, which has a next higher or lower order than the order of the first bending vibration and is out of time phase with the first bending vibration by 90°, at the optical member.
On the other hand, the second bending vibration should be different in time phase with the first bending vibration by exactly 90° to generate a stabilized traveling wave at the optical member. Further, a higher voltage should be applied to the piezoelectric element to remove a foreign substance by generating a traveling wave at the optical member, than a voltage applied to remove a foreign substance by generating a stationary wave at the optical member.
However, exciting the first bending vibration and the second bending vibration in such a manner that the second bending vibration fails to be different in time phase with the first bending vibration by exactly 90° may result in breakage of the optical member.